Aluminum-silicon base sintered porous bearing metals

ABSTRACT

ALUMINUM BASE SINTERED BEARING METALS HAVING VARIOUS ADVANTAGES CAN BE OBTAINED FROM METAL POWDERS PARTICULARLY INCLUDING 5 TO 50% BY WEIGHT OF SILICON. IT HAS BEEN FOUND THA THE ADDITION OF SILICON SUBSTANTIALLY REDUCES THE TENDENCY OF ALUMINUM BASE METALS TO CAUSE HEAT SEIZURE AND HELPS TO PREVENT THE SURFACE CLOGGING OF THE SINTERED PRODUCT. ALSO, THE METAL MIXTURE TO BE SINTERED INCLUDING SILICON POWDER HAS AN IMPROVED COMPACTIBILITY.

F 7, 173 TAKEO SEGAWA ET AL 3,728,89

ALUMINUM-SILICON BASE SINTERED POROUS BEARING METALS Filed Aug. 13, 1970Cfl fficient of friction Japan Filed Aug. 13, 1970, Ser. No. 63,429Claims priority, application Japan, Aug. 22, 1969, 44/66.002 Int. Cl.B22f 1/00 US. Cl. 29-4825 4 Claims ABSTRACT OF THE DISCLOSURE Aluminumbase sintered bearing metals having various advantages can be obtainedfrom metal powders particularly including 5 to 50% by weight of silicon.It has been found that the addition of silicon substantially reduces thetendency of aluminum base metals to cause heat seizure and helps toprevent the surface clogging of the sintered product. Also, the metalmixture to be sintered including silicon powder has an improvedcompactibility.

This invention relates to sintered porous bearing metals and moreparticularly to metals formed by sintering the metal mixtures including5 to 50% by weight of silicon powder, 0.5 to 6% by weight of copperpowder, 1 to 4% by weight of tin powder, 0.3 to 2% by weight of magnesium powder, 0.3 to 2% by weight of antimony powder and the restaluminum powder.

Heretofore, aluminum base bearing metals of different types have beenproposed but unlike copper base or the like bearing metals, they wearvery rapidly and their bearing surface is severely roughened. This hascaused many problems in practical applications of aluminum base bearingmetals despite of their merits including lightness in weight, goodbearing-speed characteristics and cheapness.

To avoid such significant wear of aluminum-base bearing meals, theinventors have conducted various researches and found that highlywear-resistant bearing metals can be obtained by adding substantialamounts of silicon to aluminum base alloys.

In alloys containing aluminum as a major ingredient and particularlyaluminum casting alloys, it has previousbeen known that the addition ofsilicon to such alloys is effective to increase the toughness ofcastings thereof even when added in a little amount but in such castingsit has commonly been supposed that the silicon largely remains inelementary form in the metal and acts asa factor causing substantialheat of friction and thus tends to cause heat seizure to the bearingsmade of such metals. Accordingly the addition of silicon to aluminumcasting alloys has previously been very limited in amount.

The present invention resides in preparing a uniform mixture of aluminumpowder comprising 5 to 50% by weight (preferably 20 to 40% by Weight) offine silicon powder, 0.5 to 6% by weight of .copper powder, 1 to 4% byweight of tin powder, 0.3 to 2% by weight of magnesium powder, 0.3 to 2%by weight antimony powder and residue of aluminum powder and compactingsuch mixture under the pressure ranging between 0.5 and 3.0 tons persquare centimeter and then sintering at the temperature ranging between480 C. and 550 C. in a period of 5 to 60 minutes. In the metals thussintered, the silicon having a relatively high hardness of Vickers 1800is intended to serve as a major load-carrying ingredient thereby toreduce the tendency of aluminum alloys to cause heat seizure, and at thesame time to help to prevent the clogging of the sintered structurewhile improving the compactibility of the metal mixture to be sintered,for

3,723,089 Patented Apr. 17, 1973 example, so as to prevent the metalmolds from being impaired in compacting operation.

The sintered structure may be impregnated with a few percent by weightof lubricating oil or with a soft metal such as lead or tin or with alow friction synthetic resin material such as tetrafiuoroethylene resinto fill the voids in the porous structure of bearing metal wherebyimproving the fitting quality of the bearing structure and imparting aself-lubricating property thereto.

Some practical examples of the present invention will next be described.

EXAMPLE 1 Ingredient: Percent by wt.

Si ..L. 5

A1 Rest Oil content 1.0

In the above proportion, aluminum powder having a particle size of lessthan 20 mesh (Tyler) silicon powder having a particle size of less than250 mesh, and copper, tin, magnesium and antimony powders having aparticle size of less than 200 mesh respectively were mixed uniformlyand the mixture obtained was compacted under the pressure of 1.5tons/cm. and then sintered for a period of 60 minutes in a temperaturerange of from 530 C. to 540 C. in a non-oxidizing atmosphere of nitrogengas to obtain a porous sintered alloy.

The alloy was impregnated with SAE #30 motor oil and thereafter testedfor hardness and radial crushing strength constant (K). Rockwell numberF and K=18 kg./mm. were obtained.

The bearing metal was then subjected to a cumulative load on a thrusttype friction wear testing machine at the peripheral speed of 23m./min., using a mating piece formed of structural carbon steel JIS845C, in the condition that the load is increased every ten minutes by10 kg./cm. The coefiicient of friction of 0.12 and the maximumload-carrying capacity as large as 60 kg./cm. were obtained.

EXAMPLE 2 Ingredient: Percent by wt. Si 10 Mg 0.5 Sb 0.5 Al Rest Oilcontent 2.0

The particle sizes of the ingredient powders and the sintering andtesting conditions used were the same as those in Example 1. The porousalloy obtained by sintering the metal powders of the composition listedabove exhibited Rockwell number F115, K=19.5 kg./mm. coeflicient offriction of 0.10 and the maximum load-carry- The particle sizes of theingredient powders and the sintering and testing conditions used werethe same as those in Example 1. The sintered porous alloy obtained bysintering the metal mixture of the composition listed above exhibitedRockwell number F100 K=17.5 kg./ mm. coefficient of friction of 0.10 andthe maximum load-carrying capacity of 120 kg./mm.

EXAMPLE 4 Ingredient: Percent by wt. Si 30 Cu 4 Sn 3 Mg Sb 0.5 A1 RestOil content 4.0

The particle sizes of the ingredient powders and the sintering andtesting conditions used were the same as those in Example 1. Thesintered porous alloy obtained by sintering the metal mixture of thecomposition listed above exhibited Rockwell number F98, K=15 kg./mm.coeflicient of friction of 0.10 and the maximum loadcarrying capacity of160 kg./cm.

' EXAMPLE 5 Ingredient: Percent by wt. Si 40 Cu 4 Sn 3 Mg 05 Sb 0.5 A1Rest Oil content 6.0

The particle sizes of the ingredient powders and the sintering andtesting conditions used were the same as those in Example 1. Thesintered porous alloy obtained by sintering the metal mixture of thecomposition listed above exhibited Rockwell number F70, K: kg./mm.coefiicient of friction of 0.12 and the maximum loadcarrying capacity of120 kg./crn.

EXAMPLE 6 Ingredient: Percent by wt. Si 50 Cu 4 Sn 3 Mg 0 5 Sb 0.5 A1Rest Oil content 7.5

The particle sizes of the ingredient powders and the sintering andtesting conditions used were the same as those in Example 1. Thesintered porous alloy obtained by sintering the metal mixture of thecomposition listed above exhibited Rockwell number F55, K=8.0 kg./mm.coetficient of friction of 0.12 and the maximum loadcarrying capacity of100 kg./cm.

As observed from these examples, the porosity of the alloy metal, asrepresented by the weight percentage of oil impregnated and theload-carrying capacity of bearings made of such alloy increase as thepercentage of silicon contained therein increases while the hardness andradial crushing strength constant value of the metal reach to theirmaximum one when the silicon content is about 10 percent by weight.Further, the silicon contained in the aluminum alloy is effective tomake it less liable to stick while preventing the surface clogging ofthe alloy structure.

The particle size of the silicon powder used should be as small aspossible and, compared with the bearing metal obtained using a siliconpowder having a particle size of from 48 to 65 mesh, the one obtainedusing silicon powder having a particle size of less than 250 mesh wasfound excellent in porosity or oil impregnation rate (by approximately40% or more) as well as uniformity of the alloy structure.

Referring to the accompanying drawing, FIG. 1 represents aphoto-micrograph of the sintered bearing metal having the composition of20% by weight of Si, 4% by weight of Cu, 3% by weight of Sn, 0.5% byweight of Mg, 0.5% by weight of Sb, rest of Al and 3.0 by weight of oil.

The sintered porous alloy of FIG. 1 exhibits Rockwell number F100,K=17.5 kg./mm. coefiicient of friction of 0.10 and the maximumload-carrying capacity of kg./mm. silicon is represented by scattereddark areas.

FIG. 2 is a graphic diagram showing the results of the friction weartests conducted with the bearing metal of Example 3 in comparison withan oil-impregnated sintered copper base alloy on a thrust type frictionwear testing machine at the sliding speed of 23 m./ min. using a matingpiece of structural carbon steel 118 545C under a cumulative loadincreasing every ten minutes by 10 kg./cm.

The test speciments were each of a composition including 20% by weightof silicon as listed above in Example 3. In FIG. 2 curves A and Brepresent the results obtained with the bearing metals made by usingsilicon powder having a particle size of less than 250 mesh and siliconpowder, having a particle size of 48 to 65 mesh respectively, and curveC illustrates for comparison the results obtained with oil impregnatedcopper base sintered alloy of the Japanese Industrial Standard B-1581,Type 1.

As observed from the diagram, the bearing metals of the presentinvention are slightly higher in coeflicient of friction than that ofoil-impregnated copper base sintered alloy but much exceed the latter intheir load-carrying capacity. In addition, the wear of the mating memberwith the bearing metal of the present invention amounted to 0.012 gramafter minutes period of friction testing and that with the copper basemetal amounted to as much as 0.015 gram after 120 minutes period offriction testing.

As regards the proportion of silicon in the metal mixture to besintered, it has been found that about 10% by weight of silicon givesthe maximum values of hardness and radial crushing strength constant tothe bearing metal obtained and that, as the silicon percentage exceedsthe optimum point, these values gradually decrease. When the siliconcontent reaches approximately 50% by weight, they become practicallyequal to the conventional values obtainable from no addition of silicon.

In contrast the oil content rises substantially linearly as the weightpercentage of silicon increases up to about 10%. The increase of oilcontent is desirable since it causes surely reduction of the coefficientof friction, prevents heat seizure and helps to extend the bearing lifeand improve the load-carrying capacity of the hearing.

The silicon proportion should be determined also considering the desiredmechanical strengths such as radial crushing strength constant andpaying attention to the fact that any silicon percentage of less than 5%by weight is not only insufiicient to prevent the significant Wearpointed out hereinbefore or to avoid the tendency of heat seizure butalso is ineffective to prevent the surface clogging or to obtain such animprovement in compactibility as will be described later. It is also benoted that any silicon percentage exceeding 50% by weight gives rise tostrength problems and is practically unusable.

It is most recommendable to use a silicon proportion in the range offrom 5 to 50% by weight and preferably from 20 to 40% by weight.

One of the conspicuous effects of adding silicon is the improvement incompactibility, that is the effect of preventing the peeling of metalmolds used in compacting the metal powder mixture to be sintered. If nosilicon is added, said metal powder in compacting operation tends toadhere to metal molds and to impair it severely. The addition of siliconis effective to prevent adhering of the metal molds and extend theirservice life. The reason why peeling of the mold is prevented byaddition of silicon, which bring rather high hardness, is not clear butsuch effect of adding silicon has now been confirmed experimentally andis one of its effects previously never thought in the art.

It is noted that copper when added in a proportion between one and 6% byweight is most effective to increase the strength of the sinteredstructure of metals but, as its proportion exceeds 6% by Weight, itincreases the shrinkage of compacts when sintered and makes thembrittle. Addition of copper of less than one percent by weight gives nonoticeable eflect.

Tin has the effect of improving the fitting quality of the bearingmetals and is most effective to increase its strength when added in aproportion of from one to 4% by weight. Tin of less than one percent byweight has no effect on the alloy produced and that of exceeding 4% byweight causes reduction in strength thereof.

Magnesium and antimony act to improve both the sinterability of themetal mixture and the mechanical strength of the sintered productrespectively.

Even in an atmosphere of nitrogen gas of commercial purity the mixtureincluding magnesium and antimony respectively can be sintered withextreme,ease, giving a smooth and beautiful appearance on the surface ofthe sintered product in case that it includes 0.6% by weight ofmagnesium and antimony respectively. In the absence of an atmosphere ofnitrogen gas, the mixture cannot be sintered satisfactorily because thealuminum oxide film is formed on the surface of metals to be sinteredduring sintering process.

The effects described above of these ingredients, namely magnesium andantimony, start to appear when the weight percentage of eitheringredient reaches 0.3% but any proportion of these ingredientsexceeding 2% by weight has a reverse effect of reducing the strength ofthe bearing metals produced and is less effective to improve thesinterability of the metal mixture to be sintered. As for antimony ithas a further effect of preventing sweating out of the relatively lowmelting ingredients when sintered thereof.

As pointed out hereinbefore, the bearing metal of the present inventioncan be impregnated with soft metals or low friction synthetic resins aswell as with lubricating oil to fill the voids in the porous structure.Impregnation of these substances is apparently effective to impartdesired fitting and self-lubricating characteristics to the metal.Impregnation of solid subtsances such as mentioned above, however,naturally reduces the proportion in which lubricating oil can beimpregnated, thus adversely affecting the bearing service life, and isnot recommendable, for example, when the bearing metal is used withoutlubrication for a relatively long period.

In other words, such solid substances as soft metals and low frictionsynthetic resins are not to be used in place of liquid lubricants butthey have the advantageous effects of improving the fittingcharacterisitc of the bearing metal and imparting a considerableself-lubricating characteristic thereto.

Accordingly, in impregnation of solid lubricating substances asmentioned above they should be used in an amount carefully determined tosuit the intended purpose or the particular application of the hearing.In cases where the metal bearing has been impregnated with aconsiderably large amount of such solid substance under a high speed, itis necessary to lubricate the metal in a positive fashion.

For example, the sintered metal of the composition as described inExample 3 can be impregnated with over to over 20% by weight of lead.For comparison, such sintered metal impregnated with approximately 20%by weight of lead (and having the oil content accordingly reduced to 1%by weight or less) and Phosphor bronze bar Type 2 (HS H3741) cutting upinto a shape of test specimen were tested in SAE #30 motor oil using amating piece of structural carbon steel S45C, at sliding speed of 83.3m./min. under the thrust load of 30 kg./ cm. (as applied between thecontacting end surfaces of the cylindrical pieces). After 60 hours ofcontinuous running, the metal of the present invention exhibited acoefiicient of friction of 0.05 whereas the Phosphor bronze pieceexhiibted a coeflicient of friction of 0.10. Also, after the sametesting period, the wearing amount of the former was measured and foundto be 0.015 gram whereas that of the latter was found to be 0.075 gram.In view of the fact that the former bearing metal, impregnated with 20%by weight of lead, has a specific gravity of much lower than that of thelatter bearing metal and of the ratio of 1:4, it is apparent that theformer or bearing metal of this invention substantially exceeds in wearresistance even if taking the difference of the specific gravity ofbetween the former and the latter in to consideration.

From the foregoing it will be apparent that the aluminum-silicon basesintered bearing metal of the present invention has many advantages overconventional aluminum base and other bearing metals, including bettercompactibility of the metal mixture to be sintered elimination of thesignificant wear previously encountered with aluminum base metals,substantial increase in load-carrying capacity and improvement inlubricating characteristics. Further, according to the presentinvention, bearings suited to different applications can be easilyproduced by impregnating the sintered metal of the invention withappropriate solid substances such as soft metals and low frictionsynthetic resins.

What is claimed is:

1. Aluminum-silicon base porous bearing metal formed by sintering acompacted mixture consisting essentially of 5 to 50% by weight ofsilicon powder, 0.5 to 6% by weight of copper powder, 1 to 4% by weightof tin powder, 0.3 to 2% by weight of magnesium powder, 0.3 to 2% byweight of antimony and the rest aluminum powder.

2. Porous bearing metal as claimed in claim 1 characterized in that itis impregnated with a soft metal, said soft metal being selected frommaterials of the group consisting of lead powder and tin powder.

3. Porous bearing metal as claimed in claim 1 characterized in that itis impregnated with low friction synthetic resin, said low frictionsynthetic resin being tetrafluoroethylene resin.

4. A process for manufacturing aluminum-silicon base sintered porousbearing metal mixture by compacting the mixture consisting essentiallyof 5 to 50% by weight of silicon powder, 0.5 to 6% by weight of copperpowder, 1 to 4% by weight of tin powder, 0.3 to 2% by weight ofmagnesium powder, 0.3 to 2% by weight of antimony powder and the rest ofaluminum powder under the pressure ranging between 0.5 and 3.0 tons persquare centimeter and then sintering in a temperature ranging between480 C. and 550 C. in a non-oxidizing atmosphere.

References Cited UNITED STATES PATENTS 1,944,183 1/ 1934 Kempf et al.-200 2,801,462 8/1957 Wagner et al. 29182.1 3,325,279 6/1967 Lawrence etal. 75-226 BENJAMIN R. PADGETT, Primary Examiner B. H. HUNT, AssistantExaminer US. Cl. X.R.

